[OMPT] Frame information for openmp taskwait

For pragma omp taskwait the runtime is called from the task context.
Therefore, the reentry frame information should be updated.

The information should be available for both taskwait event calls; therefore,
set before the first event and reset after the last event.

Patch by Joachim Protze
Differential Revision: http://reviews.llvm.org/D17145

llvm-svn: 260674